In an ultra wideband (UWB) communication system receiving a lot of interest in a recent communication system, there has been a need for developing an antenna having a more wide band characteristics, since an impulse signal is radiated and received to/from an air.
Conventionally, an inverted L antenna has been introduced for use in an UWB system.
FIG. 1 is a diagram showing one of conventional inverted L antennas in accordance with a prior art.
As shown, the conventional inverted L antenna 100 includes an antenna element 120 coupled to an edge portion A, represented by a dotted circle, of a printed circuit board (PCB) 110. The PCB 110 includes a metal layer 111, a dielectric layer 113 and a ground layer 115. An output signal is electrically passed to the antenna element 120 through a feeding line 130.
The conventional inverted L antenna 100 radiates a microwave for communicating with other communication system by using an electric field excited at the edge portion A, which is called as an exciting area of the PCB 110.
FIG. 2 is a graph showing a performance of the conventional inverted L antenna based on a S11 parameter characteristic, wherein the graph is plotted the change of S11, representing a ratio between an amount of signal inputted the inverted L antenna and an amount of signal reflected from the inverted L antenna, in response to a frequency.
As shown, although a height-to-length (H/L) ratio of the inverted L antenna becomes very low, the inverted L antenna is outperformed in antenna efficiency, a voltage standing-wave ratio (VSWR) and an antenna gain deviation.
FIG. 3 is a graph of a gain of a conventional inverted L antenna versus a radiation frequency thereof, wherein a solid line represents an absolute value of the gain, whereas a dotted line represents gain characteristics of a component of radiation wave polarized along a direction of the antenna element.
In FIG. 3, the gain of absolute value is compared to the gain of the component of radiation wave polarized along a direction of antenna element. The gain characteristic of the conventional inverted L antenna shows that a mass electric field of a polarization component vertically polarized to the direction of the antenna element is strongly excited at a high frequency range. That is, the electric field strongly excited at the edge portion A of the PCB 110 generates an interference with the polarization of the antenna element. The gain characteristic causes to reduce a receiving performance.
Therefore, a receiving sensitivity of the conventional inverted L antenna becomes to decrease, which will, in turn, limit a communication area when the conventional inverted L antenna is applied to the UWB communication system.